ALTHOUGH raunchy as ever, the third entry in the hit romantic comedy series about an on-again, off-again relationship shows signs of fatigue.

The dialogue is dirtier than ever, and the gags outrageous, and yet, like the two central characters and the seven-year relationship they labor to keep alive, “Love Off the Cuff” shows signs of fatigue as Hong Kong auteur Pang Ho-cheung runs out of anything stunningly new to say in the third film in his urban romantic comedy series. Even so, the movie packs Pang’s trademark humor, plenty of colloquial Cantonese wordplay, and a stream of cameos by dishy starlets — all of which should guarantee a robust box office in Hong Kong, but a meh reaction on the mainland.

Pang, who started out as a whiz kid making off-color indie comedies, shot “Love in a Puff” in 2010 as a snarky rejoinder to a new anti-smoking law in Hong Kong. The protagonists, Sephora-lady Cherie (Miriam Yeung) and ad-man Jimmy (Shawn Yue) were chainsmokers who meet while huddling over a garbage-can. The film became a sleeper hit, spawning the sequel “Love in the Buff,” which relocated events to Beijing as the couple kept falling in and out of love. By 2017, they have returned home from their expat stint and settled into the convenience of cohabitation. Neither wussy Jimmy nor chronically insecure Cherie feels ready to take things to the next stage.

Like “Love in the Buff,” the film kicks off with a shaggy-dog story that exemplifies Pang’s lurid imagination and his gift for juggling clashing tones. As the story evolves, the monster comes to symbolize Cherie’s underlying phobia of men and their womanizing nature. That cautionary tale segues into a midnight outing by a reservoir, where Cherie and Jimmy’s harmless desire to catch a glimpse of UFOs goes obscenely wrong, yielding the biggest howler in Pang’s entire repertoire.

The next snafu to hit their relationship occurs when Jimmy takes their Old English Sheepdog for a stroll, resulting in a horny hook-up that triggers all of Cherie’s jealousy and apprehension about their situation. Her world is then turned upside-down by visits from two unwanted relatives: her father (Paul Chun), who walked out on her mother, and Jimmy’s sexually forthright godmother (Jiang Mengjie) from Toronto.

Few Hong Kong helmers have explored commitment blues to the extent that Pang has, laying bare lovers’ calculations and narcissism with brutal honesty, while making such traits seem almost endearing. By collaborating with such woman writer-directors as Heiward Mak (“Love in a Puff”) and Luk Yee-sum (“Love in the Buff”), he succeeds in capturing the authentic perspectives of both genders within his ribald relationship studies — another plus — though it’s rare to encounter quite so many female-delivered obscenities on Hong Kong screens, which gives the sassy characters attitude, while imbuing the film with a realistic contemporary edge.

Pang, along with co-writers Luk and Jimmy Wan, expose the pitfalls lurking under the comfort zone of a long relationship with whip-smart observations and quirky details, as when Cherie tries to compensate for being a few years older than Jimmy by getting a henna job in a certain grey area. The more serious side of her age-based obsession reveals itself through her feelings that he will never grow up.

If only Cherie had been given the screen time and emotional arc to understand her own fears and work through the couple’s impasse, the film might have gained genuine heft. Instead, it’s filled with outlandish gags comprising anything from turd jokes to alien encounters, while an attempt to explain away Cherie’s self-doubt and mistrust in men via a childhood trauma is so simplistic and hackneyed. Even though a singalong in the finale is infectious and moving, one expects something more out-of-the-box from Pang.

As in the old couple Yeung and Yue play, the duo’s chemistry just gets better with every episode. Other performances are feisty across the board, especially from a gaggle of Cherie’s close friends, a coven of single fortysomething ladies whose withering comments about men serve as a Greek chorus of doom while providing the film with some of its sharpest wisecracks.